The round Cocoon nebula is seen at the lower left of the image and the long dark nebula Barnard 168 is seen extending from it across the image to the top-right. The Cocoon is primarily a red emission nebula (Sharpless-125) but does have blue reflection and dark components as well.

The Cocoon Nebula is about 15 light-years across and surrounds the young, open star cluster Collinder 470. It lies some 4,000 light-years away in the northern constellation of Cygnus (the Swan), while it is approaching us at approximately 17.8 kilometers per second.

This stellar nursery is actually a “blister” on the front edge of a large molecular complex. It combines an emission nebula of red, glowing, hydrogen gas and a reflection nebula, seen as blue, dust-reflected starlight at the edge of an otherwise invisible molecular cloud, cut by long, dark, dusty filaments where stars are forming (which can only be seen at infrared wavelengths).

The open cluster it surrounds is made up of mostly young, hot stars which clear out a cavity in the molecular cloud’s star forming dust and gas. One of them, the bright star near the center of this nebula has a surface temperature of 18 000 to 20 000 degrees and is primarily responsible for lighting up the nebula. This star is likely only a few hundred thousand years old, while the two or three hundred other stars in the area have a range of ages averaging a million or so years, suggesting that several episodes of star formation took place in the region, continuing to the present day.

This color view of the Cocoon Nebula traces remarkably subtle features within and surrounding the dusty stellar nursery.

A dark sky is probably the most important factor in observing this nebula. It appears as a diffuse round glow in small telescopes. In larger instruments hints of dark lanes can be glimpsed against the otherwise smooth haze.